BehaviorSubject

Normally Subscription means an arrangement to receive something . Similarly, in Angular applications Observables will be connected to observers and whenever they observe a new value or change in data, they will execute code with the help of Subscription and all the subscribed components will receive the updated outcome.

The Subscribe operator is the glue that connects an observer to an Observable . In order for an observer to see the items being emitted by an Observable, or to receive error or completed notifications from the Observable, it must first subscribe to that Observable with this operator.

The RxJS first() operator waits until the first value is emitted from an observable and then automatically unsubscribes , so there is no need to explicitly unsubscribe from the subscription.

The RxJS Subscribe operator is used as an adhesive agent or glue that connects an observer to an Observable . An observer must be first subscribed to see the items being emitted by an Observable or to receive an error or completed notifications from the Observable.